TWI588240B - Fluorocarbon molecules for high aspect ratio oxide etch - Google Patents

Description

Fluorocarbon molecules for high aspect ratio oxide etching [Cross-Reference to Related Applications]

The present application claims priority to U.S. Application Serial No. 61/720,139, filed on Jan. 30,,,,,,,

The present invention discloses an etching gas for plasma etching high aspect ratio via holes, gate trenches, stepped contacts, capacitor holes, contact holes, and the like in a Si-containing layer on a substrate. The present invention also discloses a plasma etching method using the same.

In memory applications in the semiconductor industry, such as DRAM and 2D NAND, plasma etching removes germanium-containing layers, such as SiO or SiN layers, from semiconductor substrates. For novel memory applications, such as 3D NAND (Hwang et al. US 2011/0180941), it is critical that the high aspect ratio etch a stack of multiple SiO/SiN or SiO/poly-Si layers. Preferably, the etchant has a high selectivity between the mask and the layer to be etched. In addition, the etchant preferably etches the structure such that the vertical features are straight and unbent. The 3D NAND stack can include other germanium containing layers.

Conventionally, plasma etching is performed using a plasma source that produces an active material from a gas source such as a gas containing hydrogen, oxygen, or fluorine. The active material then reacts with the Si-containing layer to form a fluorocarbon barrier overcoat layer and volatile materials. The volatiles are removed in the reactor by a low pressure maintained by a vacuum pump. Preferably, the active material does not etch the masking material. The masking material can comprise one of: a photoresist, amorphous carbon, polysilicon, metal or other hard mask that is not etched.

Conventional etching gases include cC ₄ F ₈ (octafluorocyclobutane), C ₄ F ₆ (hexafluoro-1,3-butadiene), CF ₄ , CH ₂ F ₂ , CH ₃ F, and/or CHF ₃ . These etching gases can also form a polymer during etching. The polymer acts as a protective layer on the sidewalls of the patterned etched structure. The polymeric protective layer prevents ion and radical etched sidewalls that can create non-vertical structures, bends, and dimensional changes. A link between F:C ratio, SiO:SiN selectivity and polymer deposition rate has been established (see, for example, Lieberman and Lichtenberg, Principles of Plasma Discharges and Materials Processing, Second Edition, Wiley-Interscience, A John Wiley & Sons Publication). , 2005, pp. 595-596; and Figure 5 of US 6387287 to Hung et al., which shows that decreasing the F/C ratio increases the coverage selectivity for nitrides).

Conventional dry etching methods such as chemical etching may not provide the desired high aspect ratio (>20:1) because the high pressure conditions required during chemical etching may adversely affect the formed orifice. Conventional chemistries such as C ₄ F ₈ and C ₄ F ₆ may also be insufficient to provide the desired high aspect ratio because etch manufacturers are rapidly depleting available parameters for making conventional chemicals work, such as RF power, RF. Frequency, pulse scheme and tuning scheme. Conventional chemicals no longer deposit sufficient polymer on the high aspect ratio sidewalls during the plasma etch process. In addition, the polymer C _x F _y on the sidewalls (where x and y are each independently in the range of 1-4) are susceptible to etching. Thus, the etched pattern may not be vertical and the structure may exhibit bending, dimensional changes, and/or pattern collapse.

One of the key issues in etching patterns is bending. Bending is usually covered by a mask Due to the etching of the sidewalls of the layer, the mask layer is typically an amorphous carbon material. The amorphous carbon material may be etched by oxygen radicals in the plasma, thereby causing the mask opening to become large and creating an arcuate etching structure.

US Pat. No. 6,659,774 to Trapp discloses a plasma etching method for forming a high aspect ratio contact opening through a ruthenium oxide layer. Trapp discloses etch chemistries containing nitrogen to fluorocarbon (C _x F _y ) and fluorohydrocarbon (C _x F _y H _z ) such as NH ₃ to improve corrosion selectivity and reduce streaking. A list of 35 fluorocarbon and fluorohydrocarbon chemicals is disclosed, but no structural formula, CAS number or isomer information is provided.

WO 2010/100254 to Solvay Fluor discloses the use of certain hydrofluoroolefins for various processes, including as an etching gas for semiconductor etching or chamber cleaning. The hydrofluoroolefin may comprise a mixture of at least one compound selected from the group consisting of a) and b): a) (Z)-1,1,1,3-tetrafluorobut-2-ene, E)-1,1,1,3-tetrafluorobut-2-ene or 2,4,4,4-tetrafluorobut-1-ene, and b) 1,1,1,4,4,4- Hexafluorobut-2-ene, 1,1,2,3,4,4-hexafluorobut-2-ene, 1,1,1,3,4,4-hexafluorobut-2-ene and 1, 1,1,2,4,4-hexafluorobut-2-ene.

Current state of the art vertical 3D NAND structures require extremely high aspect ratios through alternating stacked materials.

There is still a need for new etching gas compositions suitable for use in plasma applications to form high aspect ratio orifices.

Mark and nomenclature

Certain abbreviations, symbols, and terms are used throughout the following description and claims, and include: as used herein, the term "etching/etching" refers to a plasma etching process (ie, a dry etching process). , wherein ion bombardment accelerates the chemical reaction in the vertical direction to form vertical sidewalls at right angles to the substrate along the edge of the masked portion (Manos and Flamm, Plasma Etching An Introduction, Academic Press, 1989, pp. 12-13) . The etching process creates apertures in the substrate, such as vias, trenches, vias, gate trenches, stepped contacts, capacitor vias, contact vias, and the like.

The term "pattern etch" or "patterned etch" refers to etching a non-planar structure, such as a patterned mask layer, on a stack of germanium-containing layers. The term "mask" refers to a layer that is resistant to etching. The mask layer can be positioned above or below the layer to be etched.

The term "selectivity" means the ratio of the etch rate of one material to the etch rate of another material. The term "selective etch" or "selectively Selectively etch means that one material is etched more than the other, or in other words, the etch selectivity between the two materials is greater than or less than 1:1.

As used herein, the indefinite article "a" or "an" refers to one or more.

This document uses the standard abbreviations for the elements of the periodic table. It should be understood that the elements may be referred to by such abbreviations (for example, S refers to sulfur, Si refers to hydrazine, H refers to hydrogen, etc.).

As used herein, the abbreviation "NAND" refers to the "Negated AND" or "Not AND" gate; the abbreviation "2D" refers to the 2-dimensional gate structure on a planar substrate; the abbreviation "3D" Refers to a 3-dimensional or vertical gate structure in which the gate structures are stacked in a vertical direction; and the abbreviation "DRAM" refers to a dynamic random access memory.

Please note that Si-containing films such as SiN and SiO are listed throughout the specification and claims, but do not mention their proper stoichiometry. The germanium-containing layer may comprise a pure germanium (Si) layer such as crystalline Si, polycrystalline germanium (polySi or polycrystalline Si) or amorphous germanium; a tantalum nitride (Si _k N _l ) layer; or a germanium oxide (Si _n O _m ) layer. Or a mixture thereof, wherein k, l, m and n are in the range from 1 to 6. The tantalum nitride is preferably Si _k N _l , wherein k and l are each in the range of 0.5 to 1.5. The tantalum nitride is more preferably Si _l N _l . The cerium oxide is preferably Si _n O _m , wherein n is in the range of 0.5 to 1.5 and m is in the range of 1.5 to 3.5. More preferably, cerium oxide is SiO ₂ or SiO ₃ . The germanium containing layer may also be a cerium oxide based dielectric material such as an organic based or cerium oxide based low k dielectric material such as Black Diamond II or III material from Applied Materials. The germanium-containing layer may also include a dopant such as B, C, P, As, and/or Ge.

A method for etching a ruthenium containing film is disclosed. An etching gas is introduced into the plasma reaction chamber containing the substrate containing the ruthenium film thereon. The etching gas is trans-1,1,1,4,4,4-hexafluoro-2-butene; cis-1,1,1,4,4,4-hexafluoro-2-butene; Fluoroisobutylene; hexafluorocyclobutane (trans-1,1,2,2,3,4); pentafluorocyclobutane (1,1,2,2,3-); tetrafluorocyclobutane (1 , 1, 2, 2-); or hexafluorocyclobutane (cis-1, 1, 2, 2, 3, 4). An inert gas is introduced into the plasma reaction chamber. The plasma is activated to produce an activated etch gas that is capable of selectively etching the ruthenium containing film from the substrate. The disclosed method may include one or more of the following: ‧ the etching gas is trans-1,1,1,4,4,4-hexafluoro-2-butene; ‧the etching gas is cis- 1,1,1,4,4,4-hexafluoro-2-butene; ‧the etching gas is hexafluoroisobutylene; ‧the etching gas is hexafluorocyclobutane (trans-1,1,2,2,3 , 4); ‧ the etching gas is pentafluorocyclobutane (1,1,2,2,3-); ‧the etching gas is tetrafluorocyclobutane (1,1,2,2-); Hexafluorocyclobutane (cis-1,1,2,2,3,4); ‧activated etching gas selectively reacts with the cerium-containing membrane to form volatile by-products; ‧removes volatiles from the plasma chamber a by-product; ‧ an inert gas selected from the group consisting of He, Ar, Xe, Kr, and Ne; ‧ an inert gas of Ar; ‧ an etching gas mixed with an inert gas, and then introduced into a plasma reaction chamber to produce a mixture; ‧ introducing etching gas and inert gas into the plasma reaction chamber respectively; ‧ continuously introducing an inert gas into the plasma reaction chamber and introducing an etching gas into the plasma reaction chamber in a pulse form; ‧ an inert gas is introduced into the plasma reaction chamber About 50% of the total volume of the etching gas and the inert gas v to about 95% v/v; ‧ introduction of oxidant into the plasma reaction chamber; ‧ no introduction of oxidant into the plasma reaction chamber; ‧ oxidant selected from the group consisting of O ₂ , CO, CO ₂ , NO, N ₂ O and NO ₂ ; ‧ the oxidant is O ₂ ; ‧ the etching gas is mixed with the oxidant, and then introduced into the plasma reaction chamber; ‧ the etching gas and the oxidant are respectively introduced into the plasma reaction chamber; ‧ continuous to the plasma reaction chamber The oxidant is introduced and the etching gas is introduced into the plasma reaction chamber in a pulsed manner; ‧ the oxidant accounts for about 5% v/v to about 100% v/v of the total volume of the etching gas and the oxidant introduced into the plasma reaction chamber; The ruthenium-containing film comprises a layer of ruthenium oxide, ruthenium nitride, polysilicon or a combination thereof; ‧ the ruthenium-containing film contains an oxygen atom, a nitrogen atom, a carbon atom or a combination thereof; ‧ the ruthenium-containing film does not contain ruthenium carbide; The amorphous carbon layer is selectively etched; the ruthenium-containing film is selectively etched from the photoresist layer; the ruthenium-containing film is selectively etched from the polysilicon layer; and the ruthenium-containing film is selectively etched from the metal contact layer; ‧The ruthenium-containing film is a ruthenium oxide layer; ‧Selectively etched from the amorphous carbon layer a ruthenium oxide layer; ‧ selectively etches the ruthenium oxide layer from the photoresist layer; ‧ selectively etches the ruthenium oxide layer from the polysilicon layer; ‧ selectively etches the ruthenium oxide layer from the metal contact layer; ‧ selectively etches from the SiN layer a ruthenium oxide layer; ‧ a tantalum film is a tantalum nitride layer; ‧ a tantalum nitride layer is selectively etched from the amorphous carbon layer; ‧ a tantalum nitride layer is selectively etched from the patterned photoresist layer; ‧ a polysilicon layer is selected from the polysilicon layer Optionally etching the tantalum nitride layer; ‧ selectively etching the tantalum nitride layer from the metal contact layer; ‧ selectively etching the tantalum nitride layer from the SiO layer; ‧ selectively etching the tantalum oxide and tantalum nitride from the tantalum layer; ‧ producing an orifice with an aspect ratio between about 10:1 and about 100:1 in the ruthenium containing film; ‧ generating a gate trench; ‧ generating a stepped junction; ‧ generating a via hole; ‧ generating an aspect ratio a via hole between about 60:1 and about 100:1; ‧ a via hole having a diameter ranging from about 40 nm to about 50 nm; ‧ improving selectivity by introducing a second gas into the plasma reaction chamber; The second gas is selected from the group consisting of cC ₄ F ₈ , C ₄ F ₆ , CF ₄ , CHF ₃ , CFH ₃ , CH ₂ F ₂ , COS, CS ₂ , CF ₃ I, C ₂ F ₃ I, C ₂ F ₅ I and SO ₂ .

‧ The second gas is cC ₅ F ₈ ; ‧ The second gas is cC ₄ F ₈ ; ‧ The second gas is C ₄ F ₆ ; ‧ The etching gas is mixed with the second gas and then introduced into the plasma reaction chamber; An etching gas and a second gas are respectively introduced into the plasma reaction chamber; ‧ introducing a second gas of about 1% v/v to about 99.9% v/v into the chamber; ‧with a range of from about 25W to about 10,000W The RF power activates the plasma; the pressure in the plasma reaction chamber is in the range of about 1 mTorr to about 10 Torr; ‧ the etching gas is introduced into the plasma reaction chamber at a flow rate ranging from about 5 sccm to about 1 slm ‧ Maintaining the substrate at a temperature ranging from about -196 ° C to about 500 ° C; ‧ maintaining the substrate at a temperature ranging from about -120 ° C to about 300 ° C; At a temperature in the range of about -10 ° C to about 40 ° C; ‧ activating the etching gas by means of a quadrupole mass spectrometer, an optical emission spectrometer, FTIR or other free radical/ionometric measuring instrument; and ‧ generating electricity by applying RF power Pulp.

Also disclosed is a plasma etching compound selected from the group consisting of trans-1,1,1,4,4,4-hexafluoro-2-butene; cis-1,1,1,4,4,4-hexafluoro -2-butene; hexafluoroisobutylene; hexafluorocyclobutane (trans-1,1,2,2,3,4); pentafluorocyclobutane (1,1,2,2,3-); Tetrafluorocyclobutane (1,1,2,2-); or hexafluorocyclobutane (cis-1,1,2,2,3,4). The plasma etch compound has a purity of at least 99.9% by volume and a trace amount of gaseous impurities of less than 0.1% by volume. The total content of nitrogen and oxygen-containing gases contained in the traces of gaseous impurities is less than 150 ppm by volume. The disclosed plasma etching compound may include one or more of the following: ‧ the etching compound is trans-1,1,1,4,4,4-hexafluoro-2-butene; Cis-1,1,1,4,4,4-hexafluoro-2-butene; ‧ the etching compound is hexafluoroisobutylene; ‧ the etching compound is hexafluorocyclobutane (trans-1, 1, 2, 2,3,4); ‧ The etching compound is pentafluorocyclobutane (1,1,2,2,3-); ‧the etching compound is tetrafluorocyclobutane (1,1,2,2-); The etching compound is hexafluorocyclobutane (cis-1,1,2,2,3,4); ‧Oxygen-containing gas is water; ‧Oxygen-containing gas is CO ₂ ;‧Nitrogen-containing gas is N ₂ ; The plasma etch compound has a water content of less than 20 ppm by weight.

In order to further understand the nature and purpose of the present invention, reference should be made to the following embodiments, in which the same elements are given the same or similar reference numerals and wherein: FIG. 1 is trans- 1, 1, 1 , 4, The structural formula of 4,4-hexafluoro-2-butene; Figure 2 is the structural formula of cis-1,1,1,4,4,4-hexafluoro-2-butene; Figure 3 is trans- structural formula of 1,1,2,2,3,4- hexafluorocyclobutane; FIG. 4 is a cis ring structure of formula -1,1,2,2,3,4- hexafluoro-butane; FIG. 5 It is a structural formula of hexafluoroisobutylene; Fig. 6 is a structural formula of 1,1,1,2,4,4,4-heptafluoro-2-butene; Fig. 7 is 1,1,2,2,3-five The structural formula of fluorocyclobutane; FIG. 8 is a structural formula of 1,1,2,2-tetrafluorocyclobutane; FIG. 9 is a view showing an exemplary layer in a 3D NAND stack; FIG. 10 is a view showing a DRAM stack Figure of an exemplary layer; Figure 11 is a mass spectrometry (MS) plot of volume versus energy (in eV) of a portion of the material produced by C ₄ F ₆ H ₂ ; Figure 12 is plotted by C ₄ F ₈ MS plot of volume versus energy of the fraction of matter produced; Figure 13 is a plot of volume versus energy for the fraction of material produced by trans-1,1,1,4,4,4-hexafluoro-2-butene ; FIG. 14 is a drawing of isobutylene yield hexafluoro Part of the volume of material in FIG. MS energies; FIG. 15 cyclobutane SiO ₂ etching rate of oxygen flow rate (in terms sccm) of FIG trans -1,1,2,2,3,4- hexafluoro; Figure 16 is a graph of SiO ₂ etch rate versus oxygen flow rate for cC ₄ F ₅ H ₃ ; Figure 17 is a selectivity for trans-1,1,2,2,3,4-hexafluorocyclobutane for oxygen flow Figure 18 is a graph of the selectivity of cC ₄ F ₅ H ₃ versus oxygen flow rate; Figure 19 is a scanning electron micrograph (SEM) of the result of using 15 sccm cC ₄ F ₈ and anaerobic etching for 10 minutes. 20 is an SEM obtained by etching with 15 sccm cC ₄ E ₆ H ₂ and 12 sccm of oxygen for 10 minutes; FIG. 21 is an SEM using 15 sccm cC ₄ F ₅ H ₃ and 22 sccm of oxygen etching for 10 minutes; and FIG. 22 is a view Flowchart of H substitution, double bond, and the effect of adding O to C ₄ F ₈ molecules.

An etching gas for etching plasma via holes, gate trenches, stepped contacts, capacitor holes, contact holes, and the like in a germanium containing layer is disclosed. The disclosed etching gas provides higher selectivity to the mask layer and no characteristic distortion in the high aspect ratio structure.

The plasma etch gas improves the selectivity between the Si-containing layer and the masking material, reduces damage to the channel region, and reduces bending of the pattern high aspect ratio structure. The plasma etch gas can also be etched through alternating layers of polySi, SiO, and/or SiN to create vertical etch features.

The following compounds form the disclosed plasma etching gas: trans-1,1,1,4,4,4-hexafluoro-2-butene; cis-1,1,1,4,4,4-six Fluoro-2-butene; hexafluoroisobutylene; hexafluorocyclobutane (trans-1,1,2,2,3,4); pentafluorocyclobutane (1,1,2,2,3-) Tetrafluorocyclobutane (1,1,2,2-); or hexafluorocyclobutane (cis-1,1,2,2,3,4). These compounds are commercially available.

The disclosed plasma etch gas system is provided at a purity greater than 99.9% v/v, preferably at a purity greater than 99.99% v/v, and more preferably at a purity greater than 99.999% v/v. Disclosed etch gas containing a trace gas impurity of less than 0.1% by volume, which contains these trace gaseous impurities less than 150ppm by volume of nitrogen and oxygen-containing gas, such as H ₂ O and / or CO _2. The water content in the plasma etching gas is preferably less than 20 ppm by weight. The purified product can be produced by distillation and/or by passing a gas or liquid through a suitable adsorbent such as a 4A molecular sieve.

In one embodiment, the disclosed plasma etch gas contains less than 5% v/v, preferably less than 1% v/v, more preferably less than 0.1% v/v, and even more preferably less than 0.01% v/v. Any of its isomers. This specific example can provide better process repeatability. This specific example can be produced by distillation of a gas or a liquid. In an alternative embodiment, the disclosed plasma etch gas may contain one or more isomers between 5% v/v and 50% v/v to provide an improved process in the mixture of isomers. This is especially true when the separation of parameters or target isomers is too difficult or expensive. For example, an isomer mixture can reduce the need for two or more gas lines to the plasma reactor.

Figure 1 shows the structural formula of trans-1,1,1,4,4,4-hexafluoro-2-butene. The CAS number of trans-1,1,1,4,4,4-hexafluoro-2-butene is 66711-86-2. The boiling point of trans-1,1,1,4,4,4-hexafluoro-2-butene is 8.5 °C.

Figure 2 is a structural formula of cis-1,1,1,4,4,4-hexafluoro-2-butene. The CAS number of cis-1,1,1,4,4,4-hexafluoro-2-butene is 692-49-9. The boiling point of cis-1,1,1,4,4,4-hexafluoro-2-butene is 33 °C.

Figure 3 is a structural formula of trans-1,1,2,2,3,4-hexafluorocyclobutane. The CAS number of trans-1,1,2,2,3,4-hexafluorocyclobutane is 23012-94-4. The boiling point of trans-1,1,2,2,3,4-hexafluorocyclobutane is 27 °C.

Figure 4 is a structural formula of cis-1,1,2,2,3,4-hexafluorocyclobutane. The CAS number of cis-1,1,2,2,3,4-hexafluorocyclobutane is 22819-47-2. The boiling point of cis-1,1,2,2,3,4-hexafluorocyclobutane is 63 °C.

Figure 5 is a structural formula of hexafluoroisobutylene. The CAS number of hexafluoroisobutylene is 382-10-5. The boiling point of hexafluoroisobutylene is 14.5 °C.

Figure 6 is a structural formula of 1,1,1,2,4,4,4-heptafluoro-2-butene. The CAS number of 1,1,1,2,4,4,4-heptafluoro-2-butene is 760-42-9. 1,1,1,2,4,4,4-heptafluoro-2- The boiling point of butene is 8 °C.

Figure 7 is a structural formula of 1,1,2,2,3-pentafluorocyclobutane. The CAS number of 1,1,2,2,3-pentafluorocyclobutane is 2253-02-3. The boiling point of 1,1,2,2,3-pentafluorocyclobutane is 53 °C.

Figure 8 is a structural formula of 1,1,2,2-tetrafluorocyclobutane. The CAS number of 1,1,2,2-tetrafluorocyclobutane is 374-12-9. The boiling point of 1,1,2,2-tetrafluorocyclobutane is 50 °C.

Some of these compounds are gaseous at room temperature and atmospheric pressure. For non-gaseous (i.e., liquid) compounds, the gaseous form can be produced by conventional vaporization steps, such as direct vaporization or vaporization of the compound by bubbling. The compound can be fed to the vaporizer in a liquid state where it is vaporized prior to introduction into the reactor. Alternatively, the compound can be vaporized by delivering the carrier gas to a container containing the compound or by bubbling the carrier gas into the compound. The carrier gas can include, but is not limited to, Ar, He, N _2, and mixtures thereof. Bubbling with a carrier gas also removes any dissolved oxygen present in the etching gas. The carrier gas and compound are then introduced into the reactor as a vapor.

If necessary, the container containing the compound can be heated to a temperature to permit the compound to have a vapor pressure sufficient to pass into the etching tool. The container can be maintained at a temperature of, for example, from about 25 ° C to about 100 ° C, preferably from about 25 ° C to about 50 ° C. More preferably, the vessel is maintained at room temperature (about 25 ° C) to avoid heating the lines of the etching tool. Those skilled in the art recognize that the temperature of the vessel can be adjusted in a known manner to control the amount of vaporization of the compound.

The disclosed etching gas is suitable for plasma etching via holes, gate trenches, stepped contacts, capacitor holes, contact holes, etc. in one or more Si-containing layers and is compatible with current and future masking materials. Because it hardly induces damage on the mask and induces good high aspect ratio structural features. To achieve their properties, the disclosed etching gas can deposit an etch-resistant polymer layer during etching to help reduce the direct effects of oxygen and fluorine radicals during the etching process. The disclosed compounds also reduce damage to the poly-Si channel structure during etching (see U.S. Patent No. 2011/0180941 to Hwang et al.). The etching gas preferably has suitable volatility and stability during the etching process for delivery to the reactor/chamber.

The disclosed etching gas can be used to plasma etch the germanium-containing layer on the substrate. Revealed The plasma etching method can be applied to fabricate semiconductor devices such as NAND or 3D NAND gate or flash or DRAM memory. The disclosed etching gases can be used in other applications, such as different front end of the line (FEOL) and back end of the line (BEOL) etching applications. In addition, the disclosed etching gases can also be used to etch Si in a 3D Thorough Silicon Via (TSV) etch application to interconnect memory substrates on a logic substrate.

A plasma etching method includes providing a plasma reaction chamber in which a substrate is disposed. The plasma reaction chamber can be any enclosed space or chamber within the device in which the etching process takes place, such as, but not limited to, reactive ion etching (RIE), dual capacitive coupling plasma with single or multiple frequency RF sources (Dual Capacitively Coupled Plasma; CCP), Inductively Coupled Plasma (ICP) or Microwave Plasma Reactor or other type of etching system capable of selectively removing a portion of the Si-containing layer or producing an active material. One of ordinary skill should recognize that different plasma chamber designs provide different electronic temperature controls. The commercially available for plasma reaction chamber including (but not limited to) the magnetic field to Applied Materials sold by the trademark ^TM Emax strengthening or reactive ion etching under the trademark 2300 ^® Lam Research CCP dual reactive ion etcher sold by dielectric Flex ^TM Etching product family.

The plasma reaction chamber can contain one or more substrates. For example, the plasma reaction chamber can contain from 1 to 200 silicon wafers having a diameter of 25.4 mm to 450 mm. The one or more substrates can be any substrate suitable for use in the fabrication of semiconductor, photovoltaic, flat panel or LCD-TFT devices. The substrate will have a plurality of films or layers thereon, including one or more ruthenium containing films or layers. The substrate may or may not be patterned. Examples of suitable layers include, but are not limited to, germanium (such as amorphous germanium, polycrystalline germanium, crystalline germanium, any of which may be further p-doped or n-doped with B, C, P, As, and/or Ge) , cerium oxide, cerium nitride, cerium oxide, cerium oxynitride, tungsten, titanium nitride, tantalum nitride, a mask material such as amorphous carbon, an anti-reflective coating, a photoresist material, or a combination thereof. The hafnium oxide layer can form a dielectric material such as an organic based or yttria-based low k dielectric material (eg, a porous SiCOH film). An exemplary low-k dielectric material is produced by Applied Materials under the trade name Black Diamond II or III. Sold. In addition, a layer comprising tungsten or a noble metal such as platinum, palladium, rhodium or gold may be used.

The substrate may include a stack of a plurality of germanium-containing layers thereon, similar to that shown in Figures 9 and 10 . In Figure 9 , the stack of seven SiO/SiN layers is on top of the germanium wafer substrate (i.e., ONON or TCAT technology). One of ordinary skill will recognize that some techniques replace the SiN layer with a polySi layer (i.e., a SiO/polySi layer in P-BICS technology). One of ordinary skill will further recognize that the number of SiO/SiN or SiO/poly-Si layers in a 3D NAND stack can vary (i.e., can include more or less than seven of the depicted SiO/SiN layers). The amorphous carbon mask layer is on top of the seven SiO/SiN layers. The anti-reflective coating is on top of the amorphous carbon mask. The patterned photoresist layer is on top of the anti-reflective coating. The layer stack in Figure 9 reflects a layer similar to that used in 3D NAND gates. In Figure 10 , a thick SiO layer is on top of the germanium wafer substrate. The amorphous carbon mask layer is on top of the thick SiO layer. The anti-reflective coating is on top of the amorphous carbon mask. The patterned photoresist layer is on top of the anti-reflective coating. The layer stack in Figure 10 reflects a layer similar to that used in DRAM gates. The disclosed etching gas etches only the germanium-containing layer (i.e., SiO, SiN, polySi) without etching the amorphous carbon mask, the anti-reflective coating or the photoresist layer. The layers can be removed by other etching gases in the same or different reaction chambers. One of ordinary skill will appreciate that the layer stacks of Figures 9 and 10 are provided for illustrative purposes only.

The disclosed etching gas is introduced into a plasma reaction chamber containing a substrate and a ruthenium containing layer. The gas can be introduced into the chamber at a flow rate ranging from about 0.1 sccm to about 1 s1 m. For example, for a 200 mm wafer size, a gas can be introduced into the chamber at a flow rate ranging from about 5 sccm to about 50 sccm. Alternatively, for a 450 mm wafer size, the gas can be introduced into the chamber at a flow rate ranging from about 25 sccm to about 250 sccm. One of ordinary skill will recognize that the flow rate will vary from tool to tool.

An inert gas is also introduced into the plasma reaction chamber to maintain the plasma. The inert gas may be He, Ar, Xe, Kr, Ne or a combination thereof. The etching gas and the inert gas may be mixed prior to introduction into the chamber, wherein the inert gas comprises from about 50% v/v to about 95% v/v of the resulting mixture. Alternatively, an inert gas may be continuously introduced into the chamber while introducing an etching gas into the chamber in a pulsed form.

The etching gas and the inert gas disclosed by the plasma are activated to generate an activated etching gas. The plasma decomposes the etching gas into a free radical form (i.e., activates the etching gas). The plasma can be generated by applying RF or DC power. The plasma can be produced with RF power ranging from about 25 W to about 10,000 W. The plasma can be produced or present in the reactor itself. The plasma can be generated in a dual CCP or ICP mode with RF applied at the two electrodes. The RF frequency of the plasma can range from 200 KHz to 1 GHz. Different RF sources of different frequencies can be coupled and applied at the same electrode. The plasma RF pulse can be further used to control molecular scission and reaction at the substrate. Those skilled in the art will recognize methods and apparatus suitable for such plasma processing.

A quadrupole mass spectrometer (QMS), optical emission spectrometer, FTIR or other free radical/ionometric tool can measure the activated etching gas to determine the type and number of materials produced. If necessary, the flow rate of the etching gas and/or the inert gas can be adjusted to increase or decrease the number of radical species generated.

The disclosed etching gas can be mixed with other gases prior to introduction into the plasma reaction chamber or within the plasma reaction chamber. Preferably, the gases are mixed prior to introduction into the chamber to provide a uniform concentration of the incoming gas. In another alternative, the etching gas can be introduced into the chamber independently of other gases, such as when two or more gases are reacted. In another alternative, the etching gas and the inert gas are the only two gases used during the etching process.

Exemplary other gases include, but are not limited to, oxidizing agents such as O ₂ , O ₃ , CO, CO ₂ , NO, N ₂ O, NO _2, and combinations thereof. The disclosed etching gas and oxidant can be mixed together prior to introduction into the plasma reaction chamber. Alternatively, an oxidant can be introduced continuously into the chamber and an etching gas can be introduced into the chamber in pulses. The oxidizing agent can comprise from about 5% v/v to about 100% v/v of the mixture introduced into the chamber (where 100% v/v indicates the introduction of a pure oxidizing agent with respect to the continuous introduction of the alternative).

Other exemplary gases that may be mixed with the etching gas include additional etching gases such as cC ₄ F ₈ , C ₄ F ₆ , CF ₄ , CHF ₃ , CFH ₃ , CH ₂ F ₂ , COS, CS ₂ , CF ₃ I, C ₂ F ₃ I, C ₂ F ₅ I and SO ₂ . The vapor of the etching gas and the additional gas can be mixed prior to introduction into the plasma reaction chamber. The additional etching gas may comprise from about 1% v/v to about 99.9% v/v of the mixture introduced into the chamber.

The Si-containing layer and the activated etching gas react to form volatile by-products which are removed from the plasma reaction chamber. The amorphous carbon mask, the anti-reflective coating, and the photoresist layer are less reactive with the activated etching gas.

The temperature and pressure within the plasma reaction chamber are maintained under conditions suitable for the reaction of the ruthenium containing layer with the activated etching gas. For example, as required by the etching parameters, the pressure in the chamber can be maintained between about 0.1 mTorr and about 1000 Torr, preferably between about 1 mTorr and about 10 Torr, and more preferably at about 10 mA. Between about 1 Torr and more preferably between about 10 mTorr and about 100 mTorr. Similarly, the substrate temperature in the chamber can range from about -196 ° C to about 500 ° C, preferably from -120 ° C to about 300 ° C, and more preferably from -10 ° C to about 40 ° C. The chamber wall temperature may range from about -196 ° C to about 300 ° C depending on process requirements.

The reaction between the Si-containing layer and the activated etching gas causes anisotropic removal of the Si-containing layer from the substrate. A nitrogen atom, an oxygen atom and/or a carbon atom may also be present in the Si-containing layer. The removal is attributed to the physical sputtering of the Si-containing layer from the plasma ion (accelerated by the plasma) and/or the conversion of Si into a volatile species, such as SiF _X , by chemical reaction of the plasma material, where x is between 1 to 4 range.

The activated etch gas preferably exhibits high selectivity to the mask and etches through alternating layers of SiO and SiN, resulting in a bend free vertical etch feature that is important for 3D NAND applications. For other applications, such as DRAM and 2D NAND, for example, a plasma activated etch gas can selectively etch SiO from SiN. The plasma-activated etching gas is preferably self-masking layer, such as amorphous carbon, photoresist, polysilicon or tantalum carbide; or selectively etching SiO from a metal contact layer, such as Cu; or a channel region composed of SiGe or polysilicon regions. And / or SiN.

The disclosed etching process uses the disclosed etching gas to create via holes, gate trenches, stepped contacts, capacitor holes, contact holes, and the like in the Si-containing layer. The resulting orifices can have an aspect ratio ranging from about 10:1 to about 100:1 and ranging from about 40 nm to about 50 nm. diameter. For example, one of ordinary skill will recognize that via hole etching produces an aperture in the Si-containing layer having an aspect ratio greater than 60:1.

In a non-limiting exemplary plasma etching process, a controlled gas flow device is used to introduce trans-1,1,1,4,4,4-hexafluoro-2-butan into a 200 mm dual CCP plasma etch tool. Alkene. The controlled airflow device can be a mass flow controller. In the case of high boiling molecules, specific low pressure drop mass flow controllers from Brooks Automation (No. GF120XSD), MKS Instruments, etc. can be used. The pressure in the plasma reaction chamber was set to be about 30 mTorr. There is no need to heat the gas source because the vapor pressure of this compound at 25 ° C is about 1340 Torr. The distance between the two CCP electrodes was maintained at 1.35 cm and the top electrode RF power was fixed at 750 W. The bottom electrode RF power was varied to analyze molecular performance. The plasma reaction chamber contains a substrate having 24 pairs of SiO and SiN layers thereon, similar to that shown in FIG. Prior to this process, the ARC layer was removed by fluorocarbon and oxygen containing gas and the APF layer was removed by an oxygen containing gas. Argon gas was independently introduced into the chamber at a flow rate of 250 sccm. Trans-1,1,1,4,4,4-hexafluoro-2-butene was independently introduced into the chamber at 15 sccm. O ₂ was independently introduced into the chamber at 0-20 sccm to determine the optimum etching conditions. An aperture having an aspect ratio equal to or greater than 30:1 is produced which can be used as a via hole in a vertical NAND.

In another non-limiting exemplary plasma etching process, a hexafluoroisobutylene is introduced into a 200 mm dual CCP plasma etch tool using a controlled gas flow device. The controlled airflow device can be a mass flow controller. In the case of high boiling molecules, specific low pressure drop mass flow controllers from Brooks Automation (No. GF120XSD), MKS Instruments, etc. can be used. The pressure in the plasma reaction chamber was set to be about 30 mTorr. There is no need to heat the gas source because the vapor pressure of this compound at 20 ° C is about 900 Torr. The distance between the two CCP electrodes was maintained at 1.35 cm and the top electrode RF power was fixed at 750 W. The bottom electrode RF power was varied to analyze molecular performance. The plasma reaction chamber contains a substrate having a thick SiO layer thereon, similar to that shown in FIG. Prior to this process, the ARC layer was removed by fluorocarbon and oxygen containing gas and the APF layer was removed by an oxygen containing gas. Argon gas was independently introduced into the chamber at a flow rate of 250 sccm. Hexafluoroisobutylene was independently introduced into the chamber at 15 sccm. O ₂ was independently introduced into the chamber at 0-20 sccm to determine the optimum etching conditions. An orifice having an aspect ratio equal to or greater than 10:1 is produced, which can be used as a contact hole in a DRAM.

Example

The following non-limiting examples are provided to further illustrate specific examples of the invention. However, the examples are not intended to be all inclusive and are not intended to limit the scope of the invention described herein.

SAMCO10-NR using reactive ion etcher (RIE) or Lam 4520XLE ^TM High dielectric etch system (200mm dual frequency capacitively coupled plasma (capacitively coupled plasma; CCP) Ion Etching) (the LAM) the following tests.

Example 1

C ₄ F ₆ and cyclic C ₄ F _{8 were} directly injected into a quadruple mass spectrometer (QMS) and data of 10-100 eV was collected. The results are shown in Figures 11 and 12 . Fragment C ₄ F ₆ F: C ratio is less than C ₄ F ₈ fragments, thereby producing a polymer of high deposition rate and may improve the selectivity.

The polymer was deposited by introduction into the RIE plasma reaction chamber at 30 sccm under 1 sccm of argon. The indoor pressure is set to 5 Pa. The plasma is set to 300W. The polymer was deposited from cC ₄ F ₈ at 100 nm/min and exhibited an F:C ratio of 0.90. The polymer was deposited from C ₄ F ₆ at 280 nm/min and exhibited an F:C ratio of 0.76. C ₄ F ₆ exhibits a higher deposition rate and the resulting film shows a lower F:C ratio of the polymer, thereby indicating an increase in cross-linking.

Example 2

The polymer was deposited from the cyclic C ₄ F ₆ H ₂ and the cyclic C ₄ F ₅ H ₃ under the same conditions as in Example 1 (i.e., 30 sccm of etching gas, 1 sccm Ar, 5 Pa, and 300 W). The cyclic C ₄ F ₆ H ₂ and the cyclic C ₄ F ₅ H _{3 are} similar to the cyclic C ₄ F ₈ , but have replaced 2 or 3 F atoms with H. The polymer was deposited from cyclic C ₄ F ₆ H ₂ at 150 nm/min and exhibited an F:C ratio of 0.59. The polymer was deposited from cyclic C ₄ F ₅ H ₃ at 200 nm/min and exhibited an F:C ratio of 0.50. Increasing the hydrogen content on the cyclic butane molecule results in an increase in polymer deposition rate and a decrease in the F:C ratio of the resulting polymer.

Example 3

Two molecules with the same stoichiometry (ie C ₄ F ₆ H ₂ ) were injected directly into a quadrupole mass spectrometer (QMS) and data of 10-100 eV was collected. The results of trans-1,1,1,4,4,4-hexafluoro-2-butene (CAS No. 66711-86-2) are shown in FIG . The results of hexafluoroisobutylene (CAS No. 382-10-5) are shown in Fig. 14 . At higher energies, the CF ₃ fragment produced from hexafluoroisobutylene is more than trans-1,1,1,4,4,4-hexafluoro-2-butene and the C ₃ F ₃ H ₂ fragment is less than the reverse Formula-1,1,1,4,4,4-hexafluoro-2-butene. Fragment C ₄ F ₆ F: C ratio is less than C ₄ F ₈ fragments, thereby producing a polymer of high deposition rate and may improve the selectivity.

The polymer was deposited from two C ₄ F ₆ H ₂ compounds under the same conditions as in Example 1 (i.e., 30 sccm of etching gas, 1 sccm Ar, 5 Pa, and 300 W). The polymer was deposited at 250 nm/min from trans-1,1,1,4,4,4-hexafluoro-2-butene and exhibited an F:C ratio of 0.53. The polymer was deposited from cyclic hexafluoroisobutylene at 220 nm/min and exhibited an F:C ratio of 0.53.

Example 4

The following table summarizes the test results for various etching gases:

Based on these results, the lowest polymer deposition rate shows the highest F:C ratio of the resulting polymers (cC ₄ F ₈ and C ₄ F ₈ ). Polymerization between four molecules with double bonds (ie columns 2-5)

¹ cC ₄ F ₈ = octafluorocyclobutane; C ₄ F ₆ = hexafluorobutadiene; C ₄ F ₈ = octafluoro-2-butene

² 30sccm etching gas, 1sccm Ar, 5Pa and 300W

The large difference in the deposition rate (expressed in nm/min) indicates that the inclusion of double bonds does not exclusively control the polymerization. In fact, the deposition rate follows the cut more closely. In other words, molecules that produce fragments of higher F:C have reduced the rate of polymer deposition.

Example 5

The effect of increasing H on the etch rate of SiO ₂ was analyzed. A plot of SiO ₂ etch rate versus oxygen flow rate (in sccm) for trans-1,1,2,2,3,4-hexafluorocyclobutane is shown in FIG . A plot of SiO ₂ etch rate versus oxygen flow for cC ₄ F ₅ H ₃ is shown in FIG . Replacing an F with H causes the oxygen flow rate to increase and the process window to narrow.

The effect of increasing H on oxide selectivity on amorphous carbon (aC), photoresist (PR) and nitride was also analyzed. A plot of the selectivity to trans-1,1,2,2,3,4-hexafluorocyclobutane versus oxygen flow is provided in FIG . A plot of selectivity to cC ₄ F ₅ H ₃ versus oxygen flow is shown in FIG . The molecular flow rates in Figures 17 and 18 are the same as in Figures 15 and 16 (i.e., the left square data is 5 sccm of etching gas flow rate, the second diamond data from the left is 10 sccm, the second triangle from the right is 15 scorn, and the right circular data 20sccm). In FIGS. 17 and 18, solid symbols indicate yttria/resist selectivity, open symbols indicate yttria/tantalum nitride selectivity, and shaded symbols indicate yttria/amorphous carbon selectivity.

Example 6

The following table summarizes the test results for various etching gases:

Molecules were compared under conditions similar to SiO ₂ etch rate (ER 40-50 nm/min). The optimum selectivity of the etching gas and oxygen flow rate over the range of etch rates is selected. Other plasma conditions were fixed (ie, Ar = 150 sccm, 300 W, 5 Pa). The PR, aC, and N rows show the selectivity between SiO ₂ and photoresist (PR), amorphous carbon (aC), and tantalum nitride (N). Based on these results, and especially cC ₄ F ₈ , 23102-94-4 (trans-1,1,2,2,3,4-hexafluorocyclobutane) and 2253-02-3 (1,1, As a result of 2,2,3-pentafluorocyclobutane, an increase in H increases the selectivity of the mask. In addition, although 66711-86-2 (trans-1,1,1,4,4,4-hexafluoro-2-butene) and 382-10-5 (hexafluoroisobutylene) have the same stoichiometry (ie, C ₄ F ₆ H ₂ ), but different structures produce significantly different results.

Example 7

The effect of increasing the H content when etching a portion of the DRAM pattern stack is analyzed. The partial DRAM patterned stack consists of an anti-reflective coating (ARC29a-0.8kÅ), a ruthenium oxynitride layer (1.0kÅ), an amorphous carbon layer (3.5kÅ), and a P6100 on a 4 micron SiO ₂ substrate (Silox). The pattern (2.9kÅ) is composed. Argon gas was introduced at 150 sccm. The chamber was maintained at 5 Pa. The SAMCO RIE is set to 300W. A scanning electron micrograph of the results using 15 sccm cC ₄ F ₈ and anaerobic etching for 10 minutes is provided in FIG . Scanning electron micrographs of the results of etching with 15 sccm cC ₄ F ₆ H ₂ and 12 sccm of oxygen for 10 minutes are provided in FIG . Scanning electron micrographs of the results of etching with 15 sccm of cC ₄ F ₅ H ₃ and 22 sccm of oxygen for 10 minutes are provided in FIG . As seen in the figures, increasing H promotes a tapered feature and results in a loss of etch rate (590 nm → 380 nm → 270 nm). Increasing the H content maintains a narrow groove. There is a 110 nm trench in Figure 21 prior to etching, which is increased to 270 nm by cC ₄ F ₆ H ₂ and increased to 260 nm by cC ₄ F ₈ .

Example 8

Figure 22 is a flow chart showing the effect of H substitution, double bond, and addition of O to C ₄ F ₈ molecules. C ₄ F _{8 is} shown in the upper left corner of FIG . When two or three F atoms are displaced with a hydrogen atom (moving from left to right along the top column), it is seen that the selectivity between SiO and the mask increases and the rate of polymer deposition increases. However, increasing the H molecule also requires an increase in O ₂ dilution. When replacing two F atoms with a double bond (even if the molecule changes from saturation to unsaturated) (moving from the middle of the first column to the right of the second column), it can be seen that the polymer deposition rate increases but the selectivity and O ₂ dilution requirements are similar. . The addition of oxygen results in poor selectivity and no polymer deposition (moving down the line on the left side of the page). When the fluorine atom is replaced with a hydrogen atom on the oxygen-containing molecule (the lower left side of the page), it is seen that the selectivity and the polymer deposition rate increase, but the process window becomes narrow.

Example 9

Measurement of cyclic C ₄ F ₈ (octafluorocyclobutane), C ₄ F ₆ (hexafluoro-1,3-butadiene) and linear C ₄ F ₆ H ₂ (CAS 66711-86-2) Deposition and etch rate.

The power or RF power of the Lam etching system was set to 750 W and the bias power was set to 1500 W. The pressure is set to 30 mTorr. The distance between the plates was set to 1.35 cm. Oxygen was introduced at a flow rate of 15 sccm. Argon gas was introduced at a flow rate of 250 sccm. Each etching gas was introduced at 15 sccm. The results are shown in the table below:

66711-86-2 (trans-1,1,1,4,4,4-hexafluoro-2-butene) has better selectivity between cerium oxide and amorphous carbon than the conventional cC ₄ F ₈ , The cerium oxide etching rate is similar. The deposition rate of 66711-86-2 is also higher than cC ₄ F ₈ .

Example 10

The etching rates of 1,1,1,2,4,4,4-heptafluoro-2-butene on SiO ₂ , SiN, p-Si (polycrystalline germanium) and aC (amorphous carbon) were measured.

The power or RF power of the Lam etching system was set to 750 W and the bias power was set to 1500 W. The pressure is set to 30 mTorr. The distance between the plates was set to 1.35 cm. At 15sccm

⁴ cC ₄ F ₈ = octafluorocyclobutane; C ₄ F ₆ = hexafluorobutadiene

Introduce oxygen at a rate. Argon gas was introduced at a flow rate of 250 sccm. 1,1,1,2,4,4,4-heptafluoro-2-butene was introduced at a flow rate of 15 sccm. 1,1,1,2,4,4,4-heptafluoro-2-butene etched the SiO ₂ layer at a rate of 550 nm/min. 1,1,1,2,4,4,4-heptafluoro-2-butene etched the SiN layer at a rate of 150 nm/min. 1,1,1,2,4,4,4-heptafluoro-2-butene etched the p-Si layer at a rate of 50 nm/min. 1,1,1,2,4,4,4-heptafluoro-2-butene etches the ac layer at a rate of 75 nm/min. 1,1,1,2,4,4,4-heptafluoro-2-butene showed good selectivity between SiO ₂ and p-Si and ac.

While the invention has been shown and described with respect to the specific embodiments of the present invention, it may be modified by those skilled in the art without departing from the spirit of the invention. The specific examples described herein are illustrative only and not limiting. Many variations and modifications of the compositions and methods are possible and are within the scope of the invention. Therefore, the scope of protection is not limited to the specific examples described herein, but is only limited by the scope of the following claims, which should include all equivalents of the subject matter of the patent application.

Claims (23)

A method of etching a ruthenium-containing film, the method comprising introducing an etching gas into a plasma reaction chamber containing a substrate having a ruthenium-containing film, wherein the etching gas is selected from the group consisting of: trans-1, 1, 1, 4,4,4-hexafluoro-2-butene; cis-1,1,1,4,4,4-hexafluoro-2-butene; hexafluoroisobutylene (CAS No. 382-10-5) Pentafluorocyclobutane (1,1,2,2,3-); and tetrafluorocyclobutane (1,1,2,2-); introducing an inert gas into the plasma reaction chamber; and activating electricity The slurry produces an activated etching gas capable of selectively etching the germanium-containing film from the substrate. The method of claim 1, further comprising removing volatile byproducts from the chamber, wherein the activated etching gas selectively reacts with the ruthenium containing film to form volatile by-products. The method of any one of the preceding claims, wherein the inert gas is selected from the group consisting of He, Ar, Xe, Kr, and Ne. The method of any one of the preceding claims, wherein the inert gas comprises from about 50% v/v to about 95% of the total volume of the etching gas and the inert gas introduced into the plasma reaction chamber. v/v. The method of claim 1, wherein the etching gas is trans-1,1,1,4,4,4-hexafluoro-2-butene. The method of claim 1, wherein the etching gas is hexafluoroisobutylene. The method of any of claims 1 to 2, further comprising introducing an oxidizing agent into the plasma reaction chamber. The method of claim 7, wherein the oxidizing agent is selected from the group consisting of O ₂ , CO, CO ₂ , NO, N ₂ O, and NO ₂ . The method of claim 7, wherein the oxidant is introduced into the plasma reaction chamber The etching gas is from about 5% v/v to about 100% v/v of the total volume of the oxidant. The method of claim 7, wherein the etching gas is trans-1,1,1,4,4,4-hexafluoro-2-butene. The method of claim 7, wherein the etching gas is hexafluoroisobutylene. The method of any one of the preceding claims, wherein the ruthenium-containing film comprises a layer of ruthenium oxide, ruthenium nitride, polysilicon or a combination thereof. The method of claim 12, wherein the ruthenium containing film further comprises an oxygen atom, a nitrogen atom, a carbon atom or a combination thereof. The method of claim 12, wherein the ruthenium-containing film is selectively etched from the amorphous carbon layer. The method of claim 12, wherein the ruthenium-containing film is selectively etched from the photoresist layer. The method of claim 12, wherein the ruthenium-containing film is selectively etched from the polysilicon layer. The method of claim 12, wherein the ruthenium-containing film is selectively etched from the metal contact layer. The method of any one of the preceding claims, wherein the method produces an orifice having an aspect ratio between about 10:1 and about 100:1 in the ruthenium containing film. The method of any one of claims 1 to 2, further comprising improving selectivity by introducing a second gas into the plasma reaction chamber, wherein the second gas is selected from the group consisting of cC ₄ F ₈ a group consisting of C ₄ F ₆ , CF ₄ , CHF ₃ , CFH ₃ , CH ₂ F ₂ , COS, CS ₂ , CF ₃ I, C ₂ F ₃ I, C ₂ F ₅ I and SO ₂ . A plasma etching compound selected from the group consisting of trans-1,1,1,4,4,4-hexafluoro-2-butene; cis-1,1,1,4,4, 4-hexafluoro-2-butene; hexafluoroisobutylene (CAS No. 382-10-5); pentafluorocyclobutane (1,1,2,2,3-); and tetrafluorocyclobutane (1) , 1, 2, 2-), the plasma etching compound A trace amount of gaseous impurities having a purity of at least 99.9% by volume and less than 0.1% by volume, wherein the total content of the nitrogen-containing and oxygen-containing gases contained in the traces of gaseous impurities is less than 150 ppm by volume. A plasma etch compound according to claim 20, wherein the oxygen-containing gas is water and the plasma etch compound has a water content of less than 20 ppm by weight. A method for selectively etching a ruthenium oxide film from an amorphous carbon substrate, the method comprising: introducing a trans-1,1,1,4,4,4-hexafluoro-2-butene etching gas to the amorphous a plasma reaction chamber containing the ruthenium oxide film on the carbon substrate; introducing an inert gas into the plasma reaction chamber; and selectively etching the ruthenium oxide film from the amorphous carbon substrate by activating the plasma. A method for selectively etching a hafnium oxide film and a tantalum nitride film from a tantalum layer, the method comprising: introducing a hexafluoroisobutylene etching gas into a plasma reaction chamber containing the tantalum oxide film and a tantalum nitride film on a substrate Introducing an inert gas into the plasma reaction chamber; and selectively etching the hafnium oxide film and the tantalum nitride film from the tantalum layer by activating the plasma.